1. Field of the Invention
The present invention relates to a printed wiring board. More particularly, this invention relates to a printed wiring board having indications thereon that provide information such as the types or kinds of electronic devices to be mounted on the printed wiring board as well as the product information of the printed wiring board and others. This invention also relates to a method for producing such printed wiring boards.
2. Description of the Prior Art
There have previously been proposed printed wiring boards each comprising a substrate, conductor circuits provided on the insulated surface or surfaces of the substrate, and insulation cover coating such as solder resist provided on the substrate to protect the conductor circuits, the insulation cover coatings has colored indications of an insulation ink material comprising letters, marks, numbers or signs providing information of the types or kinds of electronic devices to be mounted on the printed wiring board as well as other information.
In such a prior art printed wiring board, the colored indications are provided on the outer insulation cover coating after the provision of the insulation cover coating on the substrate.
There have also been proposed printed wiring boards, in each of which a portion or portions of the conductor circuits are exposed from the insulation cover coating, serving as an alignment mark for the substrate and/or as connector (mounting) sections for mounting electronic devices on the pointed wiring board.
Such a prior art, printed wiring board as introduced in the above, however, does not provide a good "sliding" performance, an important requirement for smoothly feeding printed wiring boards in a process for mounting electronic devices on the substrates in Express Mail Label No. TB661440538US an automated production line. One reason for the poor "sliding" performance is that the indications printed on the insulation cover coating of a printed wiring board "protrude" from the insulation cover coating, making the surface or surfaces of the printed wiring board "rough" and often prevent smooth automatic feeding of the printed wiring board into an electronic device mounting process by causing friction with other printed wiring boards piled together, thus causing users much trouble. Further, the indications on the printed wiring board may be scraped off partially or wholly by the rubbing caused with other printed wiring boards in such a feeding step or at other times so that users of the printed wiring board are unable to read the indications easily or at all.
Generally, conductor circuits are given a light color, such as golden color, by gilding. Substrate alignment marks prepared by the same gilding are also light colored. Generally, insulation coating has a dark color, such as dark green. Therefore, indications such as letters, marks, numbers and signs provided on insulation coating are light colored, such as in white or yellow, in order to facilitate reading by users against the dark background of the insulation coating. Accordingly, there is often confusion between light colored alignment marks and also light colored indications caused by misrecognition of an indication for an alignment mark, which will result in slow down of manufacturing lines and thus poor productivity.
Conventionally an alignment mark is provided on a substrate in an area between the conductor circuits on the substrate, which reduces the freedom of formation of wiring patterns around the alignment mark. Therefore, "wiring freedom" for conductor circuits is reduced by alignment marks. It may be possible to provide an alignment mark with an insulation material on the insulation cover coating of a substrate to improve "wiring freedom" for conductor circuits, however, such an alignment mark may be lost as indications on the same surface may be lost as described earlier.
Alignment marks are essential in aligning substrates printed wiring boards in manufacturing lines. A lost alignment mark is practically unrecoverable. Therefore, it is essential that "clear" alignment marks are retained on substrates.
Electronic devices such as IC's and LSI's mounted on such a conventional printed wiring board are to be positioned "off" the insulation coating of the printed wiring board by the thickness or height of the indications provided or printed on the insulation coating when there exists an indication or indications beneath such an electronic device. Thus there is made a "considerable" distance between an electronic device mounted on the printed wiring board and the connector section or sections on the substrate where the electronic device is mounted. It is then required to use more solder material between the connector section or sections and the external terminals of the electronic device than when no indication exists beneath the electronic device, and/or it is required to extend the external terminals of the electronic device to come closer to the connector section or sections, both in order to attain a good connection reliability between the external terminals of the electronic device and the connector section or sections.
And, the electronic device will not be mounted in parallel with the substrate or squarely or securely on the printed wiring board if any indication exists under the electronic device, a considerable reduction of the quality of the printed wiring board. In such a situation, very reliable solder connection between the external terminals of the electronic device and the connector section or sections may not be provided. In case the electronic device is a QPF package having many terminals, if more solder material need be used to secure the connection between the terminals of the QPF package and the connector sections, "electrical bridging" may be formed between the terminals, which is fatal to the whole system.
Accordingly, it is an object of the present invention to provide a printed wiring board which can provide an excellent "sliding" property as well as prevent scraping off of the indications as well as the alignment mark or marks provided on the printed wiring board.
It is another object of the present invention to provide a printed wiring board that provides "clear distinction" between an alignment mark or marks and indications.
It is still another object of the present invention to provide a printed wiring board that provides reliable connection between the electronic devices mounted on the printed wiring board and the conductor circuits of the printed wiring board.
It is a further object of the present invention to provide a printed wiring board that provides an improved "wiring freedom" for conductor circuits.
It is another object of the present invention to provide a method of making such printed wiring boards.